1. Field of the Invention
The present invention relates to coiled tubing used in earth borehole operations such as oil and gas well drilling and servicing. More particularly, the present invention relates to a system and method for transporting and using coiled tubing.
2. Description of Prior Art
The widespread and expanding use of coiled tubing in earth wellbore operations such as in the drilling and/or servicing of oil and gas wells is well known. The use of coiled tubing minimizes the time and expense typically involved in using jointed pipe or jointed tubing. Additionally, coiled tubing can be used with a variety of downhole equipment such as stabilizers, drill motors, bits, well servicing tools, etc.
A typical coiled tubing rig comprises a reel of coiled tubing mounted on a platform or vehicle, an injector to run the tubing into and out of the well, a gooseneck or guide affixed to the injector for guiding the coiled tubing between the reel and the injector, a lifting device to support the injector and gooseneck, a hydraulic power pack to provide power to the reel and the injector and to other hydraulic equipment, and surface equipment such as strippers and blowout preventers to seal around the coiled tubing as it is run into and out of the well. The carrier used to transport the reel is typically a trailer or skid. The reel may be of various sizes, depending upon the size of the coiled tubing to be reeled thereupon, and the length of coiled tubing to be carried.
In the early applications of coiled tubing use, the coiled tubing was of a relatively small diameter, typically approximately 1″ OD. The use of such small diameter tubing provided the maximum amount of tubing which could possibly be mounted on a reel to be transported to and from the well site. This is important, because the size of the reel which can be transported to the well site is limited by regulations governing the roads over which the reel is to be transported, i.e., the height and width dimensions of a load transversing such roads is controlled. Thus, there is an inherent limitation on the length of coiled tubing that can be transported over such government regulated roads, etc. Further, the use of such small diameter coiled tubing limits the flow of fluids there through, limits the amount of compressive force that can be transmitted through the string of tubing to the well, limits the amount of tension that can be placed on the string of tubing, limits the amount of torque that the tubing can withstand and limits the type and weight of tools that can be used and, increasingly important, limits the length of tubing that may be used.
To overcome some of the difficulties noted above, larger sizes of coiled tubing have come into use, in diameters ranging up to 4½ inches, or even greater. However, the use of such large diameter coiled tubing with small reels designed for the smaller diameter tubing creates problems. As noted above, the size (height and width) of the reel on which the coiled tubing is shipped is limited primarily by government regulation of roads over which the tubing is to be shipped. Accordingly, under current regulations even large diameter tubing must be shipped on relatively small diameter reels. This severely limits the length of such large diameter tubing that can be moved to a site. Additionally, it is common that the tubing used at the well site is on the same reel on which it was shipped. This can involve repeated reeling and unreeling of large diameter coiled tubing on a small reel, increasing the fatigue from bending stresses.
Whether it be small diameter, e.g., 1″, or large diameter, e.g., 4½ inch or greater, coiled tubing, under current government regulation of roads on which the tubing is to be shipped, the amount of coiled tubing on a reel is limited for a reel with a given size vis-a-vis core diameter and winding space on the reel. Thus, more smaller diameter tubing can be reeled and shipped than larger diameter tubing. Stated differently, the smaller the diameter of the tubing, the larger the length of tubing that can be shipped on a given reel. There is an increasing desire to use coiled tubing, regardless of its size, in deeper and deeper wells. However, with the present system, regardless of the diameter, a single reel of coiled tubing typically does not contain a long enough length of tubing to achieve the desired depth of some deeper wells, necessitating that some sort of field splicing be employed to achieve the desired longer length. It is well known that splicing is time consuming and potentially dangerous since the integrity of the splice is typically considerably less than the integrity of the coiled tubing itself.